Add QJSEngine::registerModule

Some applications that use JavaScript as a scripting language may want
to extend JS through C++ code. The current way to do that is with
global objects.
ES6 provides a better way of encapsulating code: modules.
registerModule() allows an application to provide a QJSValue as a named module.
Developers familiar with Node.js will find this very easy to use.

Example:
```c++
QJSValue num(666);
myEngine.registerModule("themarkofthebeast", num);
```
```js
import badnews from "themarkofthebeast";
```

[ChangeLog][QtQml][QJSEngine] Adds the ability to register QJSValues in
C++ as modules for importing in MJS files.

Change-Id: I0c98dcb746aa2aa15aa2ab3082129d106413a23b
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 17 insertions, 0 deletions

diff --git a/src/qml/jsruntime/qv4engine.cpp b/src/qml/jsruntime/qv4engine.cpp
index 69db5efd05..0c3f16651a 100644
--- a/src/qml/jsruntime/qv4engine.cpp
+++ b/src/qml/jsruntime/qv4engine.cpp
@@ -879,6 +879,10 @@ ExecutionEngine::ExecutionEngine(QJSEngine *jsEngine)
 ExecutionEngine::~ExecutionEngine()
 {
     modules.clear();
+    for (auto val : nativeModules) {
+        PersistentValueStorage::free(val);
+    }
+    nativeModules.clear();
     qDeleteAll(m_extensionData);
     delete m_multiplyWrappedQObjects;
     m_multiplyWrappedQObjects = nullptr;
@@ -2072,6 +2076,19 @@ QQmlRefPointer<ExecutableCompilationUnit> ExecutionEngine::loadModule(const QUrl
     return newModule;
 }
 
+void ExecutionEngine::registerModule(const QString &_name, const QJSValue &module)
+{
+    const QUrl url(_name);
+    QMutexLocker moduleGuard(&moduleMutex);
+    const auto existingModule = nativeModules.find(url);
+    if (existingModule != nativeModules.end())
+        return;
+
+    QV4::Value* val = this->memoryManager->m_persistentValues->allocate();
+    *val = QJSValuePrivate::asReturnedValue(&module);
+    nativeModules.insert(url, val);
+}
+
 bool ExecutionEngine::diskCacheEnabled() const
 {
     return (!disableDiskCache() && !debugger()) || forceDiskCache();